I was surfing developer.ubuntu.com, searching for Unity-Human-Interface-Design-Guidelines or a Unity-HIG, but I didn't find anything. I've seen design.ubuntu.com, but that's not what I'm talking about.

Has Canonical provided Human-Interface-Design-Guidelines (HIG) for Unity apps? If not, they should! This is important if we want to have consistent and high-quality applications for our platform. Apple, Microsoft and Google have all provided such guidelines for developers of their respective platforms. GNOME has also provided an HIG-book for their developers.

What Unity apps? there's only 1 Unity app and it's Unity, i.e. Nautilus is not part of Unity is part of the Gnome Desktop thus it follows Gnome's HIG, Firefox follows Mozilla's, etc.
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Uri HerreraAug 23 '12 at 6:23

Agree with Uri Herrera, i guess what you are asking is about Global Menu Integration and Quiklist for Unity DE Developed apps .
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atenzAug 23 '12 at 6:34

Please comment if this is not what you are looking for.
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atenzAug 23 '12 at 6:42

1

Close but then again not exactly what I'm looking for. Some of the above links include guidelines, but others are just descriptive articles about different aspects of the Unity shell. Take a look at GNOME's HIG or Android's HIG that I have linked in my question ... that's the kind of stuff I'm looking for, which seems such a thing is not available for Unity.
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Seyed MohammadAug 23 '12 at 7:34

But still nothing for the desktop. Many suggest that GNOME's HIG are the guidelines for Ubuntu's desktop interface, but those guidelines are suited for the GNOME-3 desktop which is pretty much different from Unity.

Canonical is recently too much busy with Ubuntu Touch & Ubuntu Edge projects, which has turned it's focus to mobile platforms. But maybe in the future, we will see some attention returning to the desktop sector ... hopefully!

There is exactly nothing like AppleHIG in Ubuntu. Unity is default desktop of ubuntu and it is a shell for Gnome3. The Unity desktop is developed using AyatanaProject. Ayatana is itself UnityHIG, or as far as publicly available.